Fluorescent lights have long been known in the art, and have in recent years received significant attention due to their relatively low power consumption and low heat output. Fluorescent lamps are used to provide illumination in typical electrical devices for general lighting purposes because they are more efficient than incandescent bulbs in producing light. A fluorescent lamp is a low pressure gas discharge source, in which light is produced predominantly by fluorescent powders activated by ultraviolet energy generated by a mercury plasma forming an arc. The lamp, usually in the form of a tubular bulb with an electrode sealed into each end, contains mercury vapor at low pressure with a small amount of inert gas for starting. The inner walls of the bulb are coated with fluorescent powders commonly called phosphors. When the proper voltage is applied, the plasma forming an arc is produced by current flowing between the electrodes through the mercury vapor. This discharge generates some visible radiation. The ultraviolet light in turn excites the phosphors to emit light.
Two electrodes are hermetically sealed into the bulb, one at each end. These electrodes are designed for operating as either “cold” or “hot” cathodes or electrodes, more correctly called glow or arc modes of discharge operation. Electrodes for glow or cold cathode operation may consist of closed-end metal cylinders, generally coated on the inside with an emissive material. “Cold” refers to electrodes that do not rely on additional means of thermonic emission besides that created by the electrical discharge through the tube. In contrast, hot cathode fluorescents include an electrode in the form of a filament, heated with current passing there through, which provides enhanced emissions from the lamp.
Conventional cold cathode lamps operate at a current on the order of a few hundred milliamps, with a high cathode fall or voltage drop, something in excess of 50 volts. CCFLs are not appreciably affected by starting frequency because of the type of electrode used. CCFLs emit light in the same way as do standard hot electrode lamps. In general, the latter type operate as normal glow discharges and their electrodes are uncoated hollow cylinders of nickel or iron.
The cathode fall is high and to obtain high efficacy or power for general lighting purposes, conventional lamps are made fairly long, about 2–8 feet, with a diameter of about 25–40 millimeters. About 2000 volts is required for starting these conventional lamps and about 900 to 1000 volts for running. The advantages of CCFLs compared with the hot electrode fluorescent lamps are that they typically have a very long life, in consequence of their rugged electrodes, lack of filament and low current consumption. They start fairly quickly, even under cold ambient conditions. Their life is unaffected by the number of starts. Also, they may be dimmed to relatively low levels of light output.